A delivery pipe is a peripheral part of engine. However, the conventional delivery pipe, mainly prepared by a method of aluminium dye casting, has recognized several disadvantages in that a) manufacturing process is complicated, b) the weight of a product is increasing, and c) when metal materials are applied, their heat conduction is large and then, increasing gasoline temperature of the pipe plays a role to increase a total internal pressure within a fuel system, thus leading to reduction of engine efficiency and environmental problems due to gasoline discharge.
In order to comply with the aforementioned problems the conventional delivery pipe face, i.e., a) more simplified manufacturing process, b) reduced weight of product, c) enhancement of engine efficiency, and d) prevention of gasoline discharge, therefore, it is advisable to use plastic materials. The first priority for plastication of the delivery pipe should be placed on mechanical durability such as strength and rigidity, when metal materials are replaced and in addition to that, on impact-resistance and vibration-resisting properties during the driving. Further, since gasoline fuel is always filled within the delivery pipe, metal-substitute materials should be selected from gasoline-resisting ones, which may minimize the discharging amount of gasoline to the outside via internal walls of the pipe.
In order to meet the above requirements, the conventional metal materials used in a delivery pipe may be replaced by a resin such as polyamide resin, one of the engineering plastics. Since the common polyamide resin within its molecules contains amide group having a strong binding force, it exhibit a high melting point and remarkable mechanical strength. Among the engineering plastics, polyamide resin is a material with a wide scope of use and recently, it has been widely used in some parts of automobiles, electrics and electronics.
In particular, in parallel with the recent trends of favoring smaller automobiles, the demand for polyamide resin has been on a drastic increase. Now that much attention has focused on the additional properties of polyamide resin together with basic advantages, the development of novel polyamide materials is now in very active status.
When the conventional polyamide resin is applied as an automobile part, its most common manufacturing process is that after mixing the polyamide resin with various types of polyolefin resin, the polyolefin resin in fibrous or tabular form is present in the product and several layers with different properties exist towards the direction of the product, thus having a resistance against the infiltration or penetration of gasoline. Further, another method designed to enhance the resistance against gasoline has been suggested in such a manner that with the addition of a polar resin such as polyvinyl acetate to the polyamide, more large resistance may be induced by the penetration of non-polar gasoline. However, the above method has recognized some disadvantages in applying peripheral parts of engine, since the addition of components having a poor thermal stability resulted in unstable heat resistance or reduced mechanical strength at high temperature. To overcome the poor thermal stability, some reinforcing agents (e.g., glassfiber or mineral) have been added so as to improve a thermal deformation temperature and bending strength but when these agents are applied, the gasoline-resisting property, being obtained from non-reinforcing materials, is not expected due to the fact that the multilayer structure having remarkable penetration effects is destroyed.
The main reasons why the parts manufactured by glassfiber-reinforced polyamide resin shows their poor infiltration against gasoline is that 1) if there are a poor adhesive force in the interface between glassfiber and polyamide resin, gasoline vapor become diffused from the resulting interfacial crevices, and 2) gasoline, which is infiltrated into the amorphous areas of polyamide resin is delivered.
The aforementioned reasons have supported the following hypothesis in that the poor adhesive power in the interface can be ascertained by weight gains or reduced strength due to infiltration of gasoline; and in the case of second factor, the gasoline-resisting property may be increased, when the degree of crystallization of polyamide resin components using a crystal nucleating agent.
During these experiments, it has been ascertained that the improvement of gasoline-resisting property has been made available when a resin of same composition is injected at somewhat low temperature and in parallel with increase of injection rate even at a same resin temperature. As a result of analyzing the above matter, it has been noted that from the common parts where the resin flow occurs towards the rectangular direction of the product thickness, better gasoline-resisting property has been induced by enhanced orientation of glassfiber more than in the case of somewhat reduced orientation. Based upon such results, the inventor et al. have performed various experiments designed to enhance the orientation degree of glassfiber in terms of resin's own properties instead of injection conditions.
In order to enhance the orientation of glassfiber followed by increasing the viscosity of polyamide resin, therefore, experiments for the enhancement of viscosity have been performed using various types of additives via their reaction with the amine or carboxyl terminal of polyamide but the improvement of gasoline-resisting property has not eventually been shown. The inventor et al. has concluded that such poor gasoline-resisting property may occur, since the reaction of molecular terminals reduced the. crystallization of polyamide resin components and gasoline is infiltrated into the amorphous areas and thus, have completed this invention with the following conclusion that a method of using plural polyamide resins with different properties of melting flow is the most useful in improving the gasoline-resisting property, instead of a method to improve the viscosity via reaction of terminal groups.
In an effort to provide the polyamide resin with thermal stability, the inventor et al. has performed extensive studies Lo overcome the poor gasoline-resisting property induced by adding glassfiber as a reinforcing agent and in consequence, have successfully the polyamide resin composition having improved gasoline-resisting property by dint of enhancement of orientation degree of glassfiber using plural polyamide resins with different properties of melting flow.